1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer. More particularly, it pertains to a process for producing a styrenic polymer having a high degree of syndiotactic configuration efficiently and inexpensively.
2. Description of the Related Arts
In recent years, there has been proposed a process for producing a styrenic polymer having a syndiotactic configuration (hereinafter sometimes referred to as "SPS") by polymerizing a styrenic monomer by means of a catalyst comprising a transition metal compound as a primary ingredient, especially a titanium compound and an alkylaluminoxane (refer to Japanese Patent Application Laid-Open No. 187708/1987).
There has also been proposed a process for efficiently producing such a styrenic polymer (SPS) by the use of a catalyst comprising a coordination complex compound composed of an anion in which a plurality of radicals are bonded to a metal and a cation, while dispensing with an aluminoxane which is expensive and is to be used in a large amount (refer to Japanese Patent Application Laid-Open Nos. 249503/1992, 249504/1994, etc.)
However, the use of the above-mentioned catalyst for the purpose of polymerizing a styrenic monomer involves the problems that the catalytic activity deteriorates resulting in an increase in the amounts of residual metals contained in the styrenic polymer thus produced and causing a decrease in the molecular weight of the resultant styrenic polymer or a deterioration of the hue of the same and that the amounts of the residual metals need to be reduced, thus complicating the production process of the polymer, for example, an increase in the number of steps, whereby the production cost of the polymer is unreasonably increased.
As a result of intensive research and investigation made by the present inventors under such circumstances, it has been found that in the case of polymerizing a styrenic monomer by bringing a catalyst for producing SPS into contact therewith, an indene-based compound which is contained in the styrenic monomer exerts significant effect on the catalytic activity of the catalyst. The present invention has been accomplished on the basis of the above-mentioned finding and information.